Downhole cables with both fiber and copper elements

ABSTRACT

Provided is a method of manufacturing a downhole cable, the method including, forming a helical shape in an outer circumferential surface of a metal tube, the metal tube having a fiber element housed therein, and stranding a copper element in a helical space formed by the metallic tube. Also provided is a downhole cable including, a metallic tube having a helical space in an outer circumferential surface thereof, wherein the metallic tube has a fiber element housed therein, and a copper element disposed in a helical space formed by the steel tube. Double-tube and multi-tube configurations of the downhole cable are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No.60/823959, filed on Aug. 30, 2006, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Apparatuses and methods consistent with the present invention relate toa downhole hybrid cable, and more particularly to a downhole hybridcable that has both fiber and copper elements.

2. Description of the Related Art

Hybrid cables with fiber and a copper wire are used for variouspurposes. For example, they are used for supplying power via the copperwire while sensing is carried out on the fiber. Also, sensing can becarried out via the copper wire as well. Such hybrid cables have alsobeen employed in logging cables for downhole use. The logging cables aremeant to be put into, for instance, an oil well to collect samplemeasurements of the well structure. After completion of themeasurements, and verifying that the data has been collected, thelogging cable is pulled out of the oil well.

The existing technology for downhole hybrid type cables that have bothfiber and copper elements includes (1) a center fiber/gel filledstainless steel tube with copper wire wrapped around the tube and aninsulation layer around the copper wire/tube configuration which isproduced by Gulf Coast Downhole Technologies located in Houston, Tex.Another existing structure (2) has a center insulated copper wire withsmall plastic fiber/gel filled tubes with an insulation around it. Thisstructure (2) is made by Draka.

The disadvantage of item (1) is that the copper wire 6 is not easilysegregated from the stainless steel tube. Attaching sensing elements tothe cable when the cable is terminated, i.e. stripped back, is a taxingprocedure. The user needs to ensure that the copper wire is separatedfrom the stainless steel tube and it has to be re-insulated as theinsulation has to be removed to get to the copper wires. Anotherdisadvantage is that the center stainless steel tube has to be of such asize that the excess fiber length (EFL) in the tube must be relativelylow, in the case where a multi-mode optical fiber is deployed in it.This fiber is commonly used for temperature sensing, so it is often usedin this type of tube. Single mode optical fiber is also used in well forsensing. It is less sensitive than multi-mode optical fiber so theexcess fiber can be slightly higher but given that multi-mode and singlemode optical fiber is commonly deployed in the same cable, the excessfiber length will be driven by the multi-mode fiber. If the stainlesssteel tube is approximately 0.080 inches or smaller, then the EFL canonly be 0.10 to 0.15% with respect to the length of the fiber in thecore in order to still have good optical performance. This limits theamount of strain that the cable can see before the fiber is also understrain. This can be an issue for environments where the cabletemperature will be elevated.

More particularly, in downhole fiber optic cables, a ¼″ metal tube isused to house the fiber optic core. With this diameter and the ¼″ tube'swall thickness, typically 0.028″ or 0.035″, the inside diameter of the¼″ metal tube is fixed. This results in the cable designer needing towork in a small space to house the desired copper and fiber elements. Inorder to fit a 0.080 inch fiber filled stainless steel tube into this ¼″tube and to include copper elements with the appropriate insulationlevel to ensure proper performance of the copper, the size of thestainless steel tube is limited.

In general, as the stainless steel tube size increases, more excessfiber can be put into it and still have acceptable optical performance(too much excess fiber can create optical loss). Excess fiber is neededin the stainless steel tube to ensure good optical performance duringtemperature changes in, for example, the oil well. As the temperatureincreases, the metal expands faster than the fiber, and in the case thatthere is no excess fiber in the stainless steel tube, the fiber would beunder strain as the temperature increased. Increased strain reducesfiber life, can increase attenuation (optical loss), and can affectother attributes on the fiber. In the unitube configuration of item (1),with copper wire wrapped around the tube, the geometry is such that thecenter stainless steel tube is small, i.e., 0.080 inches or less. Thisis a drawback to this type of design since the center stainless steeltube size limits the EFL in the tube.

Item (2) overcomes the EFL issues of item number 1 by stranding theplastic tubes around the insulated copper wire. However, due to the sizeof the plastic tubes, the amount of benefit is limited. The strandingprovides for radial movement of the fibers in the tube which increasesthe amount of cable strain experienced by the plastic tubes before thefiber sees strain. However, with this structure, the disadvantage isthat the inherent strength of the structure is limited because thestrength element of the structure is only the center copper wire. Thisbecomes problematic as processing tensions on the core and installationpractices can result in high tension levels on the cable, thus exposingthe fiber to strain. Another disadvantage of item (2) is its crushresistance. The plastic tube is limited in the amount of external forcethat can be applied to it, in order to still have good opticalperformance.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention overcome the abovedisadvantages and other disadvantages not described above. Also, thepresent invention is not required to overcome the disadvantagesdescribed above, and an exemplary embodiment of the present inventionmay not overcome any of the problems described above.

The present invention provides a downhole cable that increases a strainfree window of the downhole cable.

The present invention also provides a downhole cable which can beelongated by tension or temperature, without excessively straining anoptical fiber within an element in the downhole cable.

The above and further objects of the present invention are furtheraccomplished by providing a method of manufacturing a cable includingforming a helical shape in an outer circumferential surface of a metaltube, the metal tube having a fiber element housed therein, andstranding a copper element in a helical space formed by the metal tube.

The metal tube may be a fiber gel filled stainless steel tube or it canbe free of gel.

According to yet another aspect of the present invention, there isprovided a cable including a metal tube having a helical shape in anouter circumferential surface thereof, wherein the metal tube has afiber element housed therein, and a copper element disposed in a helicalspace formed by the metal tube.

According to yet another aspect of the present invention, there isprovided a method of manufacturing a cable, the method including placinga first metal tube, and a second metal tube parallel to the first metaltube such that a first circumferential surface of the first metal tubeis in contact with a second circumferential area of the second metaltube, in a stranding machine, positioning a first copper element and asecond copper element in interstitial areas of the first metal tube andthe second metal tube, in the stranding machine, and stranding the firstmetal tube, the second metal tube, the first copper element, and thesecond copper element together by activating the stranding machine.

The stranding further includes helixing the first metal tube, the secondmetal tube, the first copper element, and the second copper elementtogether.

Prior to the placing the first metal tube and the second metal tube, themethod further includes forming a first helical shape in the firstcircumferential surface of the first metal tube, and forming a secondhelical shape in the second circumferential surface of the second metaltube, wherein the stranding further comprises stranding the first copperelement in a first helical interstitial space of the first helical shapein the first circumferential surface and the second helical shape in thesecond circumferential surface, and stranding the second copper elementin a second helical interstitial space of the first helical shape in thefirst circumferential surface and the second helical shape in the secondcircumferential surface.

The method may further include placing a plastic extrusion on a distalend of the stranded first metal tube, the second metal tube, the firstcopper element, and the second copper element.

According to yet another aspect of the present invention, there isprovided a double-tube cable including a first metal tube, a secondmetal tube parallel to the first metal tube such that a firstcircumferential surface of the first metal tube is in contact with asecond circumferential area of the second metal tube, and a first copperelement and a second copper element disposed in interstitial areas ofthe first metal tube and the second metal tube.

According to yet another aspect of the present invention, there isprovided a multi-tube cable including a copper element, and a pluralityof metal tubes stranded around the copper wire, wherein each of theplurality of metal tubes has a fiber element therein, and covering a topend of the copper element and the plurality of metal tubes with anextrusion.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects of the present invention will be moreapparent by describing certain exemplary embodiments of the presentinvention with reference to the accompanying drawings, in which:

FIG. 1 shows a downhole hybrid type cable that includes a metal tubewith copper wire wrapped around the tube and an insulation layer aroundthe copper wire, where the metal tube is not preformed.

FIG. 2 shows a cross-section of a down hole cable according a firstexemplary embodiment of the present invention;

FIG. 3 shows a side view of the metal tube and the copper elementstranded in the helical spaces formed in the metal tube during a methodof manufacturing the down hole cable of the first exemplary embodimentof the present invention;

FIG. 4 shows another side view of the metal tube and the copper elementbeing twisted on center in the stranding process during the method ofmanufacturing the down hole cable of the first exemplary embodiment ofthe present invention;

FIG. 5 shows a performer forming the helical shape in the outercircumferential surface of the metal tube;

FIG. 6 shows a cross-section of a double-tube down hole cable accordinga second exemplary embodiment of the present invention; and

FIG. 7 shows a cross-section of a multi-tube down hole cable according athird exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Certain exemplary embodiments of the present invention will now bedescribed in greater detail with reference to the accompanying drawings.

In the following description, same drawing reference numerals are usedfor the same elements even in different drawings. The matters defined inthe description, such as detailed construction and elements, areprovided to assist in a comprehensive understanding of the invention.Thus, it is apparent that the present invention can be carried outwithout those specifically defined matters. Also, well-known functionsor constructions are not described in detail since they would obscurethe invention with unnecessary detail.

A down hole cable according to an exemplary embodiment of the presentinvention, and a method of manufacturing the down hole cable of thisexemplary embodiment, will be described with reference to FIG. 2 andFIG. 3. FIG. 2 shows a cross-section of a down hole cable according thefirst exemplary embodiment of the present invention.

The downhole cable 10-1 illustrated in FIG. 2 includes a metal tube 14,and the copper element 16, and the jacket 20 and a metallic tube 22. Asshown in FIG. 2, the metal tube 14 has a fiber element 18 housedtherein. FIG. 3 shows the metal tube 14 of FIG. 2 with a helical shape(141, 142) in a outer circumferential area thereof, and a copper element16 disposed in the helical space formed by the metal tube.

In this exemplary embodiment, the metal tube 14 is a fiber gel filledstainless steel tube, with a 0.079″ diameter. However, the metal tube 14may be made of Incoloy 825, Inconel 625, or any other metal types.

The copper element 16 is a copper wire, which is a 18 American WireGauge (AWG) conductor, having a 0.076″ diameter. The jacket 20 may be aplastic extrusion that can be placed on a top end of the metal tube 14and the copper element 16. In this exemplary embodiment, the jacket 20has a 0.169″ diameter, but the jacket 20 is not limited to thisdiameter.

The core, i.e., the metal tube 14 and the copper element 16, is put intothe metallic tube 22. The metal tube 22 may be made of Incoloy 825, 316stainless steel (SS) or any other suitable metal. The wall thickness ofthe metallic tube 22 can vary depending on desired requirements of acustomer. Common wall thicknesses are 0.028″, 0.035″ and 0.049″, but thepresent invention is not limited to these wall thicknesses. The metallictube 22 in FIG. 1 has a ¼″ diameter. The core goes into the ¼″ metallictube with a 0.035″ wall thickness. However, the core is not limited tothese thicknesses. As would be obvious to a skilled artisan, the presentinvention can be adapted for the other wall thicknesses. In thisexemplary embodiment, the down hole cable is for a fixed installation.

Next, an exemplary method of manufacturing the downhole cable shown inFIG. 2 is described with reference to FIGS. 2-5. A coated copper element16 and the metal tube 14 are put on a stranding machine. Strandingmachines are well known in the art. The copper element 16 and the metaltube 14 are on payoffs that control the tension of each element toensure consistency in the stranding process. These two elements arerouted from their payoffs to the point where they come together. At thispoint, as shown in FIG. 5, a preformer 100 is located that the metaltube 14 goes through. This performer 100 is used for imparting apermanent helical bend in an element so it retains this shape in thecable structure. In the most common type of a performer 100, it is aseries of three rollers (102 a, 102 b, and 102 c) that a subject element(the metal tube 14) will pass through with the ability to adjust thedistance from the first (102 a) to the third roller (102 c) while thesecond roller (102 b) can be adjusted to create an offset required toget the desired curvature of the subject element, in this case, themetal tube 14. As shown in FIGS. 3 and 4, a helical shape 141, 142 isformed in an outer circumferential surface of the metal tube 14 in theperforming process by the rollers 102 a, 102 b, and 102 c.

The effectiveness of subsequently stranding the copper element 16 andthe metal tube 14 together is crucially dependent on the accuracy ofperforming the stainless metal tube 14. A high level of precision isrequired in the performing process to ensure that the copper element 16and the metal tube 14 are stranded uniformly, as shown in FIG. 3. Theresultant diameter of the two stranded elements has a typical variationof <0.004″. This variation is an exemplary, non-limiting variation, andthe present invention does not require this variation as a firmrequirement for the stranded copper element 16 and the metal tube 14 tobe inserted inside the metallic tube 22. The metallic tube 22 may allowfor greater variation. To achieve this level of variation, the tensioncontrol of the two elements must be very tight and very low and be ableto control the tension on the two elements individually. In theexemplary embodiment shown in FIG. 3, performing the metal tube 14 andstranding the copper element in a helical shape formed by the metal tube14 results in a twist diameter Dt′ equal to a diameter D14 of the metaltube 14 plus the diameter D16 of the copper element 16. That is,Dt′=D14+D16. Therefore, according to this exemplary embodiment of thepresent invention, the twist diameter Dt′ is reduced by one diameterlength D16 of the copper element 16 as compared to stranding the copperelement 6 to a metal tube 4 that did not go through the preformingprocess, as shown in FIG. 1.

In particular, as shown in FIG. 1, a resulting twist diameter Dt (afterthe copper wire 6 is wrapped around the stainless steel tube 4 which hasnot been preformed, is equal to a diameter D4 of the steel tube 4 plustwo times the diameter D6 of the coated copper wire 6. That is,Dt=D4+2×D6. As such, if the metal tube 4 is not preformed, the core willneed to be inserted into a bigger outer metal tube, thereby increasingmanufacturing costs.

As the tension varies the quality of the helical shape 141, 142 formedin the metal tube 14 will degrade which will make the resultant diametervary. This is critical due to the need for the stranded copper element16 and the metal tube 14 to be inserted into the metallic tube 22 andbeing able to slide inside the tube 22 with minimal effort. If thehelical shape 141, 142 formed in the metal tube 14 is not properlyformed, that is, either the metal tube 14 is over preformed (helixdiameter is too large) or the preform is too small (resulting in anessentially straight steel tube with the copper wire wrapped around it),the two elements will be forced into position during the process ofputting them into the metallic tube 22. This results in undesiredcompression and strain on the copper element 16 and the metal tube 14,which can compromise the performance characteristics of the copperelement 16 and the fiber 18 housed in the metal tube 14.

In this exemplary embodiment, the tension for each element (the copperelement 16 and the metal tube 14) was kept different to achieve the samestrain in each element. This is because in a post processing stage, whenthe copper element 16 and the metal tube 14 are in a relaxed state ornon-tensioned state, the two elements will relax by the same amount sothe resulting linear length of these elements are the same. If this wasnot done, the element that had a lower strain with respect to the otherelement would flex out of position to absorb the resultant compressionimparted from the higher strained other element. This can result inprocessing issues during the process to add a plastic jacket 20 to thetwo elements and in putting the two elements into the metallic tube 22.If an element among the copper element 16 and the metal tube 14 had alower strain with respect to the higher strained element, the lowerstrained element can flex out of position and can be damaged in a numberof ways. For example, it may get caught on production equipment orfolding over itself, especially with the copper wire.

After the metal tube 14 is preformed, it continues to what is called theclosing point where the copper element is also routed. As shown in FIG.4, since the copper element 16 is significantly less stiff than thestainless metal tube 14, the copper element 16 will conform to the helixof the stainless steel tube. In other words, the metal tube 14 and thecopper element 16 are twisted concentrically on center as shown in FIG.4. After this point, the two elements, which are now stranded together,are routed to the takeup of the machine.

In this exemplary embodiment, each of copper element 16 and the metaltube 14 have a diameter of approximately 0.078″ in diameter. After thesetwo elements are stranded together, they then get a plastic extrusion 20over them to hold them together. This plastic is not required in theexemplary embodiment, but can be provided as an optional feature. Thediameter over the extrusion is approximately 0.171″. This structure thengoes into, e.g., the ¼″ metallic tube 22 with a wall thickness of 0.035″so the resultant inside diameter of the ¼″ metallic tube is 0.180″. Thestructural dimensions are not critical and can be adjusted to otherelement sizes, i.e. different copper element 16 and fiber filledstainless metal tube 14 dimensions, and the outer tube 22 does not needto have a ¼″ diameter nor a 0.035″ wall thickness.

Next, a double-tube downhole cable according a second exemplaryembodiment of the present invention, and a method of manufacturing thedouble-tube downhole cable will be described with reference to FIG. 6.

FIG. 6 shows a cross-section of a double-tube down hole cable 10-2according the second exemplary embodiment of the present invention.

As shown in FIG. 6, the downhole cable 10-2 includes a first metal tube14 a, a second metal tube 14 b, wherein both the first metal tube 14 aand the second metal tube 14 b have the fiber element 18 housed therein.The downhole cable 10-2 further includes a first copper element 16 a anda second copper element 16 b.

As shown in FIG. 6, the second metal tube 14 b is positioned parallel tothe first metal tube 14 a. A first circumferential surface of the firstmetal tube 14 a is in contact with a second circumferential area of thesecond metal tube 14 b. The first and second copper elements (14 a and14 b) are disposed in interstitial areas 24 of the first metal tube 14 aand the second metal tube 14 b.

The plastic jacket 20 holds the first metal tube 14 a, the second metaltube 14 b, the first copper element 16 a, and the second copper element16 b are held together by the plastic jacket 20. This combination canthen be inserted into the metallic tube 22, similar to the downholecable illustrated in FIG. 2.

The characteristics of the first metal tube 14 a, the second metal tube14 b, the first copper element 16 a, the second copper element 16 b, theplastic jacket 20, and the metallic tube 22 can vary as discussed abovewith respect to FIG. 2. For example, in this exemplary embodiment, thecopper element 16 can be a 21 AWG conductor. The diameter of the firstmetal tube 14 a, and the second metal tube 14 b can be 0.046″, but isnot limited to this limitation.

To manufacture the double-tube downhole cable 10-2 shown in FIG. 6, thefirst metal tube 14 a, the second metal tube 14 b, the first copperelement 16 a, and the second copper element 16 b are stranded togetherat the same time. Each of the elements 14 a, 14 b, 16 a, and 16 c areplaced on a stranding machine. At the point where these elements wouldcome together, tooling in the stranding machine is designed to controldesired positions of the subject elements. Once the first metal tube 14a, the second metal tube 14 b, the first copper element 16 a, and thesecond copper element 16 b are in the desired positions, i.e., the firstmetal tube 14 a and the second metal tube 14 b are in contact with eachother, and the first copper wire 16 a and the second copper wire 16 bare situated in the interstitial areas of the first metal tube 14 a andthe second metal tube 14 b, they are stranded together to form the core.This stranding method is called planetary stranding where the individualelements are stranded in such a way that they are not twisted on theirown axis but are wrapped with the other elements

Unlike the cable 10-1 of the first exemplary embodiment shown in FIG. 2,in the double-tube cable 10-2 of this exemplary embodiment, the metaltube 14 a and the second metal tube 14 b do not have to go through thepreforming process shown in FIG. 5. The preforming of the first metaltube 14 a and the second metal tube 14 b can be an optional feature.Preforming the first metal tube 14 a and the second metal tube 14 b isnot needed when the tube 14 a and the tube 14 b have the samecharacteristics. As these components 14 a, 14 b, 16 a, and 16 c arehelixed, they twist on center, resulting in a uniform twisting.Therefore, in this case, the diameters of the first copper element 16 aand the second copper element 16 a would not contribute to the diameterof the resultant diameter of the stranded components (14 a, 14 b, 16 a,and 16 b), since they are placed in helical interstitial spaces of thefirst metal tube 14 a and the second metal tube 14 b, during thestranding process.

Next, the third exemplary embodiment of the present invention will bedescribed with reference to FIG. 7.

FIG. 7 shows a multi-tube downhole cable 10-3. The cable 10-3 includes acopper element 16′ and multiple metal tubes 14′ stranded together withthe copper element 16′. The plastic jacket 20 can be put over thestranded elements (16′,14′) to hold the elements together, to form acore. Subsequently, this core can be inserted into the metallic tube 22.

The foregoing embodiments are merely exemplary and are not to beconstrued as limiting the present invention. The present teaching can bereadily applied to other types of apparatuses. Also, the description ofthe exemplary embodiments of the present invention is intended to beillustrative, and not to limit the scope of the claims, and manyalternatives, modifications, and variations will be apparent to thoseskilled in the art.

1. A method of manufacturing a cable, the method comprising: forming ahelical shape in an outer circumferential surface of a metal tube, themetal tube having a fiber element housed therein; and stranding a copperelement in a helical space formed by the metal tube.
 2. The methodaccording to claim 1, wherein the metal tube is a fiber gel filledstainless metal tube.
 3. A cable comprising: a metal tube having ahelical shape in an outer circumferential surface thereof, wherein themetal tube has a fiber element housed therein; and a copper elementdisposed in a helical space formed by the metal tube.
 4. The cableaccording to claim 3, wherein the metal tube is a fiber gel filledstainless metal tube.
 5. A method of manufacturing a cable, the methodcomprising: placing a first metal tube, and a second metal tube parallelto the first metal tube such that a first circumferential surface of thefirst metal tube is in contact with a second circumferential area of thesecond metal tube, in a stranding machine; positioning a first copperelement and a second copper element in interstitial areas of the firstmetal tube and the second metal tube, in the stranding machine; andstranding the first metal tube, the second metal tube, the first copperelement, and the second copper element together by activating thestranding machine.
 6. The method according to claim 5, wherein thestranding further comprises helixing the first metal tube, the secondmetal tube, the first copper element, and the second copper elementtogether.
 7. The method according to claim 5, further comprising: priorto the placing the first metal tube and the second metal tube, forming afirst helical shape in the first circumferential surface of the firstmetal tube; and forming a second helical shape in the secondcircumferential surface of the second metal tube; wherein the strandingfurther comprises stranding the first copper element in a first helicalinterstitial space of the first helical shape in the firstcircumferential surface and the second helical shape in the secondcircumferential surface, and stranding the second copper element in asecond helical interstitial space of the first helical shape in thefirst circumferential surface and the second helical shape in the secondcircumferential surface.
 8. The method according to claim 5, furthercomprising: placing a plastic extrusion on a distal end of the strandedfirst metal tube, the second metal tube, the first copper element, andthe second copper element.
 9. A double-tube downhole cable comprising: afirst metal tube; a second metal tube parallel to the first metal tubesuch that a first circumferential surface of the first metal tube is incontact with a second circumferential area of the second metal tube; anda first copper element and a second copper element disposed ininterstitial areas of the first metal tube and the second metal tube.10. A multi-tube downhole cable comprising: a copper element; aplurality of metal tubes stranded around the copper wire, wherein eachof the plurality of metal tubes has a fiber element therein; andcovering a top end of the copper element and the plurality of metaltubes with an extrusion.